This invention relates to a device for measuring pressures, forces and torques and has at least three piezo-resistive resistor elements which are mechanically stressed by apparatus components and which take up forces and torques transmitted by the apparatus components.
In a known device of the above-outlined type, as disclosed, for example, in German Offenlegungsschrift (application published without examination) 36 23 391, a plurality of resistor elements are mounted on a spring disk which pivotally couples a driving unit of a handling apparatus with a tool holder. The spring disk which is secured at its edge to the drive unit and at its middle to the tool holder is deformed in response to external forces applied to the tool holder by the tool. During this occurrence the resistor elements too, undergo a deformation, resulting in a resistance signal. In such an arrangement the measuring results depend from the bias (pre-tension) and the material properties of the spring disk. These, in turn, are affected by the temperature and also by the fatigue of material after a certain service period. Also, the prior art arrangement is not adapted to measure torques because the spring disk clamped at its edge and in the middle connects the apparatus components rigidly to one another and deforms insufficiently during transmission of torques.
U.K. Published Application 2,096,777 discloses a device of the earlier-outlined type for measuring forces and torques in the x, y and z directions. According to this reference, the resistor elements are supported on the side faces of four uniformly distributed arms which couple a hub associated with one apparatus component to an outer ring associated with the other apparatus component. The joints of the arms with the outer ring are weakened in such a manner that upon appearance of a force or a torque in an axis extending through one arm pair, essentially only the other, transversely arranged arm pair is deformed, resulting in a simplification of the evaluation circuitry. In this arrangement too, the measuring results are dependent from the properties of the material of the parts which carry the measuring elements. Further, the measuring elements change their resistance only relatively slightly in case of alternating stresses.
Further, pressure measuring devices are known as disclosed, for example, in German Patent No. 3,818,191, which are provided with a single piezo-resistive resistor element orthogonally stressed by a plunger to which the pressure to be measured is applied. These devices, however, are not adapted to measure bending or rotary torques.